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Improving constraints

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Ewout Prangsma 2018-02-08 11:20:00 +01:00
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docs/constraints.md
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@ -3,10 +3,13 @@
The ArangoDB operator tries to honor various constraints to support high availability of The ArangoDB operator tries to honor various constraints to support high availability of
the ArangoDB cluster. the ArangoDB cluster.
## Run agents on separate machines ## Run agents and dbservers on separate machines
It is essential for HA that agents are running on separate nodes. It is essential for resilience and high availability that no two agents
To ensure this, the agent Pods are configured with pod-anti-affinity. are running on the same node and no two dbservers are running running
on the same node.
To ensure this, the agent and dbserver Pods are configured with pod-anti-affinity.
```yaml ```yaml
kind: Pod kind: Pod
@ -29,38 +32,28 @@ spec:
- key: role - key: role
operator: In operator: In
values: values:
- agent - agent (or dbserver)
``` ```
## Run dbservers on separate machines The settings used for pod affinity are based on the `spec.environment` setting.
It is needed for HA that dbservers are running on separate nodes. For a `development` environment we use `preferredDuringSchedulingIgnoredDuringExecution`
To ensure this, the dbserver Pods are configured with pod-anti-affinity. so deployments are still possible on tiny clusters like `minikube`.
```yaml For `production` environments we enforce (anti-)affinity using
kind: Pod `requiredDuringSchedulingIgnoredDuringExecution`.
spec:
affinity:
podAntiAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
- weight: 100
podAffinityTerm:
labelSelector:
matchExpressions:
- key: app
operator: In
values:
- arangodb
- key: arangodb_cluster_name
operator: In
values:
- <cluster-name>
- key: role
operator: In
values:
- dbserver
```
Q: Do we want to allow multiple dbservers on a single node? ## Run coordinators on separate machines
If so, we should use `preferredDuringSchedulingIgnoredDuringExecution`
antiy-affinity. It is preferred to run coordinators of separate machines.
To achieve this, the coordinator Pods are configured with pod-anti-affinity
using the `preferredDuringSchedulingIgnoredDuringExecution` setting.
## Run syncworkers on same machine as dbserver
It is preferred to run syncworkers on the same machine as
dbservers.
To achieve this, the syncworker Pods are configured with pod-affinity
using the `preferredDuringSchedulingIgnoredDuringExecution` setting.